Global disease simulation Plague, Inc is among the top-grossing and most popular games of 2012. It owes its success in part to a years-old, meaningfully-similar web game called Pandemic 2 -- but it was primarily a series of smart business decisions that made Plague, Inc the game we'll remember.

When Ndemic Creations CEO James Vaughan asked for for the thoughts of Dan Arc, Pandemic 2's developer, he said he resented the game's success initially, but regards the situation as a learning opportunity. Nor does he consider Plague Inc a clone, he has said.

James Vaughan had no involvement with games prior to launching Plague, Inc, a global pandemic simulation game for iOS and Android. "It was actually just me and three freelancers," Vaughan says.

And its success began with a completely-silent launch: Vaughan was on vacation, and Apple released the game sooner than it expected.

"That meant it was already facing a pretty significant uphill battle," he says. But in the four hours that followed its surprise launch, it had been downloaded 500 times.

"It has a simple pitch," he says. "It's a game where you have to kill everybody in the world... it makes people want to check it out and see how it works."

There aren't too many sophisticated niche strategy games on the mobile market, which means there's less competition and less worry about being drowned out by competitors or overly-similar games. With no Apple featuring, no user acquisition and no marketing, it's been able to spread to fans of the niche slowly by word of mouth.

"Community engagement is so crucial," he says. Keeping well aware of the response to one's app and its features is crucial, and having a unique name helps with the discoverability of the reaction, Vaughan notes. And the small team, with the help of family and friends, responds to all the feedback, and considers it essential.

Plague, Inc is very screenshot-ready, with witty news headlines that stream during the players quest to make the whole world ill, and with customizable messages. Because the game is so shareable -- to where fatigue about Plague Inc posts spawned its own Reddit thread -- that's key to the virality of the game.

The Center for Disease control has even invited Vaughan to come and talk about how the game models infectious disease, and how simulation games can be used to engage people. "These outside-the-app opportunities, even if they don't directly create revenue, can drive a lot of interest to your app, and can also be a lot of fun."

Relasing updates has a significant impact on chart positions; Vaughan estimates that with only one update the game would linger at an average position of 32, while multiple updates since launch improve the average to 9. Ten months after launch, a new virus update brought the game its highest-grossing day ever, he says.